Single-walled nanotubes (SWNTs) are unique molecular structures that exhibit interesting and useful properties and may be utilized for a variety of devices. SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged atoms.
SWNTs have been used in a variety of applications that are increasing in number and diversity as their manufacture and implementation becomes more widespread. For instance, single-walled carbon nanotubes have been increasingly considered for and/or used with advanced electronics applications. Carbon-based SWNTs are hollow structures composed, at least partially, of carbon atoms. Single-walled carbon nanotubes can be doped with other elements such as metals, boron and nitrogen. Such SWNTs are increasingly being used as conductors (e.g., nanowires) and to form electronic components such as field effect transistors (FETs), switches and others.
While the use of carbon nanotubes in electrical applications is growing, there are many challenges to the implementation of nanotubes for a variety of such applications. For instance, one challenge to the implementation of carbon nanotubes, and particularly to the implementation of SWNTs, relates to the tendency of SWNTs to grow in a manner that exhibits metallic and semiconducting mixtures due to various chiralities (e.g., geometric characteristics). The metallic nature of nanotubes can be undesirable for a variety of applications, including those susceptible to electrical shorting.
One electrical application that is susceptible to difficulties associated with the growth of metallic nanotubes is the field-effect transistor (FET). The scalable implementation of large numbers of semiconducting SWNTs (S-SWNTs) in parallel without electrical shorting by metallic SWNTs (M-SWNT) has been particularly difficult. Such parallel S-SWNTs and their characteristics are useful for high-current and high-speed nanotube FETs.
Previous approaches to the selective synthesis of S-SWNTs have often exhibited undesirable results. For instance, some approaches result in SWNTs with undesirably small diameters or lengths due to excessive processing, making ohmic contact difficult. Approaches involving the separation of M-SWNTs have exhibited incomplete separation, which can degrade on/off ratios for electronic devices such as FETs or other switching devices. Synthesis approaches that covalently alter M-SWNTs result in M-SWNTs that are susceptible to recovery, where altered M-SWNTs become conducting again, which can cause shorts. Recover from covalent alteration or functionalization may occur, for example, during annealing steps that are often involved in device processing. Moreover, breakdown approaches (e.g., chemical or physical approaches to break undesirable M-SWNTs), have been tedious and expensive, and are thus difficult to scale to application to hundreds or thousands of nanotube-based FETs.
The above issues as well as others have presented challenges to the manufacture and implementation of nanotubes for a variety of applications.